This invention relates to processing of font data on the basis of pattern codes and further to a drawing technique using the font data, and to a technique which will be effective when applied to a display controller and a drawing processor using character font, for example.
As the technique which handles font patterns such as characters and symbols in a display controller and a drawing processor, a character generator system and a bit block transfer system have been employed in the past as described, for example, in "LSI Handbook" published by Ohm-sha, Nov. 30, 1984, p.p. 555-556.
The character generator system is one that expresses patterns such as characters and symbols by individual codes, stores these codes in a main storage or part of the region of an image memory, reads them out sequentially on the basis of instruction from a terminal device, converts them to the patterns such as characters by a character generator consisting of pattern generating ROM (Read-Only Memory) for display.
On the other hand, the bit block transfer system is a graphic display system which expresses the patterns such as the characters and symbols in a pixel unit by regarding them as figures drawn in a predetermined rectangular region, temporarily stores them in the image as it is in a bit map memory such as a frame buffer memory and handles the image, and display is accomplished by transferring in the block unit the image data of the rectangular region corresponding to a predetermined pattern from the main storage or the non-display region of the frame buffer memory to the display region of the frame buffer memory.
In the course of studies on the two systems described above as the technique for expressing the patterns such as the characters and symbols, the inventors of the present invention have found out that in accordance with the character generator system described above, display and drawing control are made unavoidably in a rough pattern unit because the width, shape and direction of the pattern to be displayed such as the character or symbol are determined fixedly by hardware of a character generator for generating the pattern.
In contrast, the bit block transfer system is more flexible in the aspect of a pattern control function because it can control the individual patterns in the pixel unit, but is not free from the following problems. When, for example, predetermined pattern data are transferred from outside a display controller to a frame buffer memory, the data corresponding to each bit of the rectangular region, in which the necessary pattern is defined, must be transferred through a microprocessor for controlling the system as a whole, so that the load to the microprocessor cannot be reduced. Furthermore, since the time required for the data transfer increases, the speed of drawing or displaying operation cannot be improved. If the necessary pattern data is stored in the non-display region of the frame buffer memory, transfer control of the pattern data on the basis of the microprocessor is not necessary but the microprocessor must yet execute the operation of converting the pattern code designated from an external terminal to the logical address. Such a conversion operation by the microprocessor results of course in the increase in the load to the microprocessor and from this aspect, too, the drawing or display operation of the pattern such as a character cannot be sped up.